1. Field of the Invention
The present invention generally relates to a microelectromechanical system (MEMS) diaphragm and a fabricating method thereof, in particular, to an MEMS system diaphragm and a fabricating method thereof capable of reducing a residual stress in an upper electrode, enhancing a reliability and sensitivity of the upper electrode, and reducing fabricating steps.
2. Description of Related Art
Along with the progress of technology, various MEMS devices are fabricated by a micro-machining technique. For example, the MEMS devices include motors, pumps, valves, switches, sensors, pixels, diaphragms, etc.
The diaphragms manufactured by the MEMS technique (hereinafter MEMS diaphragms) have advantages of light weight, small volume, good signal quality, etc, so MEMS diaphragms increasingly become the mainstream products of mini diaphragms. Furthermore, due to the growing demands for mobile phones, the requirements on the sound-receiving quality and size minimization of mobile phones and the circuit integration level are stricter. Moreover, along with the gradual maturity of the hearing aids technique, the demands for MEMS diaphragms grow sharply.
Generally speaking, a method of fabricating a MEMS diaphragm includes forming a lower electrode, a dielectric layer, and an upper electrode in sequence on a substrate and then removing the dielectric layer between the lower electrode and the upper electrode. Furthermore, in a conventional MEMS diaphragm, usually, a material of the upper electrode is a metal. However, after the dielectric layer between the upper electrode and the lower electrode is removed, the metal material has larger residual stress, so the upper electrode is easily warped, which causes quality deterioration of the MEMS diaphragm.
Furthermore, in order to solve the problem that the upper electrode is easily warped, usually, before removing the dielectric layer between the upper electrode and the lower electrode, an etching process is performed to form meshes in the upper electrode to release a residual stress in the upper electrode. The upper electrode has the meshes, so the area of the force bearing surface is reduced when the sound pressure wave sensing of the upper electrode is performed, and thus the sensitivity is lowered. Therefore, the upper electrode is sealed by a polymer thin film in the subsequent process.
However, the polymer thin film does not have the characteristic of high temperature resistance, so the polymer thin film may be easily damaged in the subsequent high temperature process. In addition, although the method may solve the problem that the upper electrode is easily warped, the reliability of the upper electrode is reduced, and the fabricating steps are increased.